1. Field of the Invention
The invention generally relates to a pixel structure and a manufacturing method thereof, and more particularly, to a pixel structure of a plane to line (PLS) switching display and a manufacturing method thereof.
2. Description of Related Art
Currently, all TFT liquid crystal display panels on the market are developing towards high contrast, no grayscale reverse, high luminance, high saturation, fast response and wide viewing. The common wide viewing technology includes twisted nematic (TN) plus wide viewing film liquid crystal display (LCD) panel, in-plane switching (IPS) LCD panel, fringe field switching (FFS) LCD panel and multi-domain vertical alignment (MVA) LCD panel.
Taking an FFS LCD panel as an example, this kind of panel has optical characteristics of lowest viewing color distortion (i.e., low color bias) and high transmittance, so that it is widely used in various electronic equipments serving as a planar display device. Among middle and small size panels, in order to increase aperture ratio of the pixel structure thereof, a PLS panel design based on the same control principle as the FFS LCD panel has been developed now, in which the difference between the two panels rests merely in the disposing way of pixel electrode and common electrode.
U.S. Pat. No. 7,663,724B2 discloses a pixel structure design of a PLS display, in which a semiconductor layer, a pixel electrode, a source and a drain, a protective layer and a common electrode layer are sequentially formed so as to complete a pixel structure. Since according to the design, the pixel electrode is formed prior to forming the source/the drain, the source or the drain would cover a part of the pixel electrode. Moreover, after forming the source and the drain, a back-channel etch drying process is used to remove a part of the semiconductor layer located under a place between the source and the drain, which although can avoid high off current situation, but the pixel electrode easily produces residue or debris due to the plasma bombardment method during the back-channel etch drying process step. The residue or debris of the pixel electrodes may affect the component characteristic of the semiconductor layer and the flatness of the successively formed protective layer and thereby affect the display quality of the integral display. In addition, the pixel structure is fabricated by using six photomask processes, which, relatively to the currently usual five photomask processes, has a higher fabrication cost. In short, how to solve the problem caused by the residue or debris of a pixel electrode and reduce the number of employed photomasks becomes one of important developing directions.